This invention relates to a coated film with exceptional embossing characteristics and a method for producing the film.
Holograms and diffraction gratings are images that diffract light created by the texturizing of a substrate under heat and pressure. Such images are used to create decorative packaging, security products and a host of other uses. The embossed substrates are often metallized to create high contrast. Such metallized substrates are found on credit cards, membership materials, board laminates, labels, toys, packaging materials and many commodity products.
Currently, it is well known in the art to produce holograms by embossing polyvinylchloride (PVC), polyethyleneterephthalate (PET), biaxially oriented polypropylene (BOPP), polystyrene (PS), polyamides (PA) such as Nylon or other plastic materials. If the substrates are BOPP or PET it is also well known in the art to produce holographic substrates by coating a relatively thick acrylic layer on the substrate by a coating process. In the case of PET substrates, this coating is done by an off-line process as is done by hologram manufactures at the point of use of the web substrate. However, it is desirable to get a pre-coated and embossable PET film from a substrate manufacturer that can directly accept the holographic texture. Such a material would obviate the need for the hologram manufacturers to coat the base materials and will reduce overall costs of manufacturing.
Unfortunately, in order to produce a directly embossed film at the point of film manufacture, it is deemed necessary to provide a thick, embossable, surface on the PET film. Such a surface can be provided either through a co-extrusion process or, perhaps, through an inline coating process. In the case of co-extrusion, it is necessary to produce a surface layer with many of the same characteristics of PET. Therefore, IV, melt strength, melt viscosity and the like are important parameters necessary to get the co-extruded layer through the PET film making process. Typical materials that can survive this process are often analogs of PET itself. These materials suffer the problem of having low crystallinity and are, therefore, heat-sealable. A heat-sealable material will often stick to the embossing shim rendering the embossed texture of little commercial quality.
In the case of inline coating of PET film, the thickness deemed necessary to produce embossable holographic substrates are practically impossible to achieve with a film making process. A thick-coated layer will require reduced PET film making line speeds to accommodate the high water loads in a tenter oven. In addition, the presence of a thick coating on the PET film will often make recycling of coated PET film waste back into the process difficult, or in many cases impossible.
U.S. Pat. No. 4,913,858 describes the requirements of an offline coating for holographic embossing use.
U.S. Pat. No. 3,758,649 describes embossing directly into a thermoplastic sheet.
Other known publications include:
Creating Interference Colors on Thermoplastic Films Without Colorants, Trudy Bryson, Coburn Corporation, 1982
Dimension, design and printability, James Coburn
Holographic Advances Open New Dimensions For Converters, S. F. Mann, Dennison Mfg. Co. 1986
Optical Embossing, James River Products.
This invention relates to an embossable, coated polyethyleneterephthalate (PET) film including a uniaxially oriented PET base film, and a coating applied to the PET base film, wherein the coating and the PET base film have as a composite been transversely stretched, the coating resin impregnating a surface portion of the PET base film upon the transverse stretching, thereby rendering the surface portion of the film susceptible to embossing.
This invention also relates to a method of producing a coated, directly embossable polyethyleneterephthalate (PET) film including stretching a PET film to form a uniaxially oriented PET film, drying the uniaxially oriented PET film, coating at least one surface of the uniaxially oriented PET film with an aqueous solution of an organic material, and rendering at least one surface of a resulting coated uniaxially oriented PET film susceptible to direct embossing by impregnation of the surface of the uniaxially oriented PET film with at least a portion of the coating by transverse stretching the coated uniaxially oriented PET film to produce a biaxially oriented and embossable polyester film.